Self-aligning vehicular transmitter system

ABSTRACT

A method is provided for self-aligning a transmitting RF frequency between a portable transceiving device and a base station transceiving device. The base station transceiving device is mounted in a vehicle for controlling a vehicle accessory function in response to RF messages broadcast between the transceiving devices. The RF signal is transmitted from one of the portable or base station transceiving devices to the other of the portable or base station transceiving devices. The frequency of the RF signal is varied during the transmission. A RSSI value of a received RF signal is measured at selected frequencies. A respective frequency having a maximum RSSI value is determined. At least a portion of a subsequent RF message is transmitted from one of the portable transceiving device or base station transceiving device using the respective frequency.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to aligning the RF transmitting signalbetween a vehicle related transmitting device and a vehicle relatedreceiving device, and more specifically, to a remote vehicle accessorytransmitter and a vehicle based control module for aligning thetransmitting and receiving center frequencies.

2. Description of the Related Art

Transmitting devices such as remote keyless entry (RKE) fobs typicallytransmit data on a modulated signal to a receiving device such as avehicle based remote keyless entry module. The signal is modulated on acarrier wave by the RKE fob at a respective center frequency and isreceived by the RKE module that is tuned to the same respective centerfrequency.

For a two-way communication between a RKE module and a RKE fob,communication from the RKE module to the RKE fob is often limited inrange. This is primarily due to the limited size of the antenna packagedwithin the RKE fob and the limited power supply of the RKE fob. Antennasthat are small in size as that of the RKE fob combined with the RKEfob's limited power (i.e., small power supply) results in low gainthereby limiting the reception range of the RKE fob. In addition, thepower level emissions of RF transmitted signals are limited as theFederal Communications Commission (FCC) maintains regulations on themaximum emission that may be generated by respective transmitted RFsignal for a respective application.

To optimize a long-range signal transmission from the RKE module to theRKE fob having low gain, the bandwidth of the RKE fob for receiving atransmitted signal must be narrowed. The greater the distance of signaltransmission between the transmitting and receiving devices, thenarrower the bandwidth must be to receive the signal. Narrowing thebandwidth too much will not allow the received signal to fall within thereceiver bandwidth if the transmitter and receiving center frequenciesare in a mis-alignment condition. Thus it is imperative to maintain thealignment of the center frequencies between the transmitter and thereceiver when transmitting long distances. Typically the transmitter andreceiver are calibrated to a specific center frequency where a balanceis maintained between the allowable distance that a RF signal istransmitted and the allowable width that a bandwidth may be narrowedgiven the maximum allowable transmitting distance.

Under certain conditions such as temperature changes, the centerfrequency of the transmitting device may shift. Small shifts in thecenter frequency are typically tolerated by the receiving device due tothe receiving device having a sufficient bandwidth for receiving thesignal with small center frequency shifts. This allows for smalldiscrepancies in the alignment of the center frequencies between thetransmitting device and receiving device due to environmental changes orpossible circuit tolerances. Devices such as RKE modules and RKE fobstypically are permanently tuned to a respective center frequency fortransmitting and receiving signals, and as stated earlier, the RKE fobmay have a small bandwidth for receiving signals from the RKE module.Maintaining a small bandwidth at a permanently tuned center frequencymake the transmitting system susceptible to the issues described above.Even if the RKE module and RKE fob were tunable, a method would berequired to calibrate the center frequencies of the two devices.Requiring the operator to knowingly and constantly calibrate the twodevices would be burdensome.

SUMMARY OF THE INVENTION

The present invention has the advantage of self-aligning the centerfrequencies between a vehicle-based transceiving device and a portabletransceiving device during a normal operation of the two communicationdevices without requiring the operator to perform additional calibrationsteps.

In one aspect of the present invention, a method is provided forself-aligning a transmitting RF frequency between a portabletransceiving device and a base station transceiving device. The basestation transceiving device is mounted in a vehicle for controlling avehicle accessory function in response to RF messages broadcast betweenthe transceiving devices. The RF signal is transmitted from one of theportable or base station transceiving devices to the other of theportable or base station transceiving devices. The frequency of the RFsignal is varied during the transmission. A RSSI value of a received RFsignal is measured at selected frequencies. A respective frequencyhaving a maximum RSSI value is determined. At least a portion of asubsequent RF message is transmitted from one of the portabletransceiving device or base station transceiving device using therespective frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a self-tuning transmission system between a remotetransceiving device and a base station transceiving device according toa preferred embodiment of the present invention.

FIG. 2 is a circuit for varying the frequency of a RF signal accordingto a preferred embodiment of the present invention.

FIG. 3 illustrates two-way transmission signal between the between thebetween two transceiving devices according to a first preferredembodiment of the present invention.

FIG. 4 illustrates two-way transmission signal between the between thebetween two transceiving devices according to a second preferredembodiment of the present invention.

FIG. 5 is a method for self-tuning a transmission signal between aremote transceiving device and a base station transceiving deviceaccording to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a self-tuning RF transmission system between a remotetransceiving device 11 and a base station transceiving device 12. Theportable transceiving device 11 includes a transmitting circuit 15 forbroadcasting RF messages to a receiving circuit 22 within the basestation transceiving device 12. The portable transceiving device 11 mayinclude a remote keyless entry (RKE) fob for broadcasting RF messagesfor performing vehicle entry functions such as door unlock/lockfunctions, trunk unlatch, sliding door operation, and panic alarm. Theportable transceiving device 11 may also broadcast RF messages forremotely starting/stopping a vehicle engine. Furthermore, the portabletransceiving device 11 may be disposed within each of the vehicle tiresfor broadcasting data relating to the pressure of the vehicle tires.

The base station transceiving device 12 includes a vehicle based controlmodule for activating a vehicle accessory operation in response toreceiving a respective RF message such as a RKE module for activatingvehicle entry functions. The base station transceiving device 12 mayalso include a vehicle based control module for remotelystarting/stopping a vehicle engine in response to a received RF messageor provide an alert warning if tire pressure is below a predeterminedthreshold.

The portable transceiving device 11, as shown in FIG. 1, includes thetransmitting circuit 15 and a receiving circuit 16 for transmitting andreceiving RF messages (i.e., data messages) as well as RF signals (i.e.,test signals). Alternatively, the transmitting circuit 15 and thereceiving circuit 16 may be combined into an integrated circuit (e.g.,transceiver) rather than two separate integrated circuits. The receivingcircuit 16 of the portable transceiving device 11 measures a receivedsignal strength (RSSI) of a received RF signal. The RSSI is indicativeof the power of the received RF signal. A controller 17, such as amicrocontroller, processes received signals from the receiving circuit16 and controls outgoing data transmissions via the transmitting circuit15. An antenna 20 integrated within the portable transceiving device 11is provided to receive incoming RF messages and RF signals and broadcastoutgoing RF messages and RF signals. A display screen 18 is disposed inthe portable transceiving device 11 for displaying information receivedfrom the base station transceiving device 12. Such information mayinclude status information relating to a vehicle accessory function suchas doors unlocked, trunk unlatched, engine running, etc.

The base station transceiving device 12 includes a transmitting circuit21 and a receiving circuit 22. Alternatively, the transmitting circuit21 and the receiving circuit 22 may be combined into an integratedcircuit (e.g., transceiver) rather than two separate integratedcircuits. The receiving circuit 22 of the base station transceivingdevice 12 measures the RSSI of a received RF signal. The base stationtransceiving device 12 further includes a controller 23 such as themicrocontroller for processing received signals and for controlling thedata transmission of output signals. Antenna 25 is provided forreceiving incoming RF messages and RF signals and for broadcastingoutgoing RF messages and RF signals to the portable transceiving device11. Since the base station transmitting device 12 is packaged within thevehicle, the antenna 25 can be of any suitable length for receivingtransmitted signals from the portable transceiving device 11. Theantenna 20 of the portable transceiving device 11 is typically small sothat it may be packaged within the portable transceiving device 11. Itis therefore critical that for the bandwidth of the portabletransceiving device 11 be small to receive long range transmissions fromthe base station transceiving device 12.

Environmental conditions such as temperature may cause a misalignmentbetween the transmitting center frequency in the base stationtransmitting device 12 and the center frequency of the portabletransceiving device 11. To determine whether a shift in the centerfrequency of base station transmitting device 12 has occurred, a testsignal is transmitted from base station transmitting device 12 to theportable transceiving device 11 to determine the optimum transmittingcenter frequency for subsequent message transmissions.

In a preferred embodiment, the base station transceiving device 12transmits a test signal to the portable transceiving device 11. The testsignal is transmitted in response to a user actuating one of therespective vehicle accessory buttons on the portable transceiving device11. Alternatively, the self-tuning operation may be initiated bytransmitting test signals periodically at specific time intervals. Asthe test signal is transmitted to the portable transceiving device 11,the frequency of the transmission is varied. Preferably, the frequencyis varied over a plurality of discrete frequencies spanning the normalfrequency value. The receiving circuit 16 of the portable transceivingdevice 11 receives the test signal and measures an RSSI value for eachdiscrete frequency. Each measured RSSI value is provided to thecontroller 17. The controller 17 determines which discrete frequencyproduces the maximum RSSI value. The frequency associated with themaximum RSSI value is transmitted via the transmitting circuit 15 to thebase station transceiving device 12. The base station transceivingdevice 12 adjusts the transmitting frequency of the transmitting circuit21 to the respective frequency associated with the maximum RSSI value.The transmitting circuit 21 of the base station transceiving device 12maintains the center frequency at the respective frequency for allsubsequent transmissions until a next respective frequency having amaximum RSSI value is determined.

Alternatively, the respective frequency associated with the maximum RSSIvalue corresponding to test signals broadcast from base stationtransceiving device 12 to the portable transceiving device 11 may bedetermined by the controller 23. As the receiving circuit 16 receivesthe test signals, the receiving circuit measures the RSSI of eachdiscrete signal and simultaneously transmits each discrete RSSI value tothe receiving circuit 22 of the base station transceiving device 12. Thebase station transceiving device 12 receives each measured discretefrequency and the associated RSSI value and determines which respectivefrequency has a maximum RSSI value. The optimum frequency is stored inassociation with the ID of the fob and then used when messages aretransmitted to that fob.

In the preferred embodiment, the transmitting frequency of thetransmitting circuit 15 of the portable transceiving device 11 may beself-adjusted using the same method. The test signal is transmitted inresponse to a user actuating one of the respective vehicle accessorybuttons on the portable transceiving device 11. A test signal istransmitted from the portable transceiving device 11 to the base stationtransceiving device. The frequency is transmission is varied. Thereceiving circuit 22 of the portable transceiving device 12 receives thetest signal and measures an RSSI value for each discrete frequency. Eachmeasured RSSI value is provided to the controller 23. The controller 23determines which discrete frequency produces the maximum RSSI value andtransmits the frequency having the maximum RSSI value to the portabletransceiving device 11. The portable transceiving device 11 adjusts thetransmitting frequency of the transmitting circuit 15 to the respectivefrequency associated with the maximum RSSI value. The portabletransceiving device 11 of the base station transceiving device 12maintains the center frequency at the respective frequency for allsubsequent transmissions until a next respective frequency having amaximum RSSI value is determined.

Alternatively, if the portable transceiving device 11 is transmittingthe test signal to the base station transceiving device 12, thecontroller 23 of the base station transceiving device 12 measures theRSSI of each discrete signal and simultaneously transmit each discreteRSSI value to the receiving circuit 16 of the portable transceivingdevice 11. The controller 17 portable transceiving device 11 thendetermines the optimum transmitting frequency and then adjusts thetransmitting frequency of the transmitting circuit 15 to the optimumtransmitting frequency.

FIG. 2 illustrates a block diagram of a circuit for varying thefrequency of the test signal generated by either the portabletransceiving device 11 or base station transceiving device 12. Apreferred method for varying the frequency is by varactor tuning.Varactor tuning includes tuning a circuit by using a varactor diode 24to obtain a desired frequency. The varactor diode is electricallyconnected between the controller 23 and the transmitter 21. The varactordiode 24 acts as a variable capacitor to change the frequency of theoscillating signal. The controller 23 uses a digital-to-analog converterin the controller 23 to adjust the DC value supplied to the varactordiode 24. The adjustment of the DC value changes the varactorcapacitance which allows the frequency of the transmitted RF test signalto be varied. In alternative embodiments, other methods may be used tovary the frequency of the test signal such as utilizing a phase lockedloop. The varactor diode 24 may also be used to retune the transmittingfrequency of the transmitting circuit to the optimum transmittingfrequency for data transmission.

FIG. 3 illustrates a two-way transmission signal between the between thebase station transceiving device 12 and the portable transceiving device11. In the preferred embodiment, a transmitting signal is initiated bythe base station transceiving device 12 for providing status informationregarding a vehicle operation (e.g., door unlocked/locked, enginerunning, or sliding doors open) in response to a request for a vehicleentry request by the portable transceiving device 11. The transmittingsignal typically includes a data packet that contains a preamblefollowed by encoded data. The preamble includes a series of pulses,typically 0 to 5 volts, having a predetermined width between each pulse.The pulses typically signify that transmitted data is to follow. Thepreamble is used to synchronize the communication transmission betweenbase station transceiving device 11 and the portable transceiving device12. This ensures that the receiving device (portable transceivingdevice) can correctly interpret when the data transmission starts. Anidentifier 42 follows the preamble for identifying the base stationtransceiving device 41. The identifier 42 is an identification code thatprovides the necessary authentication so that the portable transceivingdevice 11 can proceed forward in communicating with the base stationtransceiving device 12. If the identification code is not authenticated,then the portable transceiving device will await for a next transmittedsignal. The next portion of transmitted data includes a test signal. Asthe test signal is transmitted, the frequency of the transmission isvaried. Each discrete signal is received by the portable transceivingdevice 11 and a respective RSSI value is measured for each discretesignal. After each discrete signal is received and the respective RSSIvalue is measured for each discrete signal, the controller 17 of theportable transceiving device 11 determines which discrete signalgenerated the maximum RSSI. A test result signal 43 (i.e., optimumtransmitting frequency) is transmitted from the portable transceivingdevice 12 to the base station transceiving device 11. After the basestation transceiving device 11 receives the test results 43, thetransmitting frequency of the base station transceiving device 11 ischanged to the frequency associated with the maximum RSSI value. Thisoptimizes the remainder of the signal transmission from the base stationtransceiving device 11 to the portable transceiving device 12. Theremainder of the messages 44 containing information regarding the statusof a respective vehicle operation is transmitted to the portabletransceiving device 11 using the optimum transmitting frequency.

FIG. 4 illustrates a two-way transmission signal between the between thebase station transceiving device 12 and the portable transceiving device11 according to a second preferred embodiment. Initially the basestation transceiving device 11 transmits the preamble and identifier 41to the portable transceiving device 12. After the base stationtransceiving device 12 is authenticated, a test signal is transmitted tothe portable transceiving device where the frequency of the transmissionsignal is varied. After each discrete signal 46 is received by theportable transceiving device 12, the RSSI value is measured for eachrespective discrete signal 46. Upon determining the RSSI value for arespective signal, the RSSI value 47 for the recently transmitteddiscrete signal is transmitted from the portable transceiving device 11to the base station transceiving device 12. As each subsequent discretesignal 46 is received by the portable transceiving device 11, theassociated RSSI value 47 for each discrete signal 46 is transmitted tothe base station transceiving device 12. After all discrete test signals46 are received and their associated RSSI values 47 are transmitted tothe base station transceiving device 12, the controller 23 of the basestation transceiving device 12 determines which frequency generated themaximum RSSI value. The transmitting frequency of the base stationtransceiving device 12 adjusts the transmitting frequency to thefrequency associated with the maximum RSSI value for optimizingsubsequent transmissions. The remainder of the messages 44 aretransmitted to the portable transceiving device using the optimizedfrequency transmission.

FIG. 5 illustrates a method for self-aligning a transmission signalbetween a portable transceiving device and a base station transceivingdevice. In step 31, a remote vehicle entry operation is initiated. Theremote vehicle entry operation may include actuating a respective buttonon a RKE fob for unlocking a vehicle door. In alternative embodiments,other vehicle-based RF applications may include engine start/stopoperations, or tire pressure monitoring. In step 32, a confirmationsignal is sent from the RKE module to the RKE fob providing status ofthe requested vehicle entry operation. A portion of the RF signaltransmitted includes a RF test signal. In step 33, the frequency of thetransmission is varied over a plurality of discrete frequencies duringthe transmission of the test signal. In step 34, the RSSI value of eachdiscrete frequency is measured. In step 35, the controller of the RKEfob determines which respective frequency produces a maximum RSSI value.In step 36, the optimum RSSI value at the respective frequency istransmitted to the RKE module. In step 37, the RKE module is tuned tothe respective frequency producing the maximum RSSI value. The optimumtransmitting frequency along with an identification code of the RKE fobis stored in the memory of the RKE module. This allows the RKE module toidentify the optimum transmitting frequency for a respective RKE fob ifmore than one RKE fob is used. In step 38, the remainder of theconfirmation message is transmitted by the RKE module to the RKE fobusing the respective frequency having the optimum RSSI value.

From the foregoing description, one ordinarily skilled in the art caneasily ascertain the essential characteristics of this invention and,without departing from the spirit and scope thereof, can make variouschanges and modifications to the invention to adapt it to various usagesand conditions.

1. A method of self-aligning a transmitting RF frequency between aportable transceiving device and a base station transceiving device,wherein the base station transceiving device is mounted in a vehicle forcontrolling a vehicle accessory function in response to RF messagesbroadcast between the transceiving devices, the method comprising saidsteps of: transmitting a RF signal from one of a portable or basestation transceiving devices to the other of the portable or basestation transceiving devices, the RF signal having a frequency thatvaries during the transmission; measuring a RSSI value of a received RFsignal at selected frequencies by the other of the portable or basestation transceiving devices; transmitting each RSSI value of eachvaried frequency as measured by the other portable or base stationtransceiving devices to the one of the portable or base stationtransceiving devices; determining a respective frequency having amaximum RSSI value, the determination being made by the one of theportable or base station transceiving devices; and transmitting at leasta portion of a subsequent RF message from the one of the portabletransceiving device or the base station transceiving device using therespective frequency having the maximum RSSI value.
 2. The method ofclaim 1 wherein the portable transceiver device includes a remotekeyless entry (RKE) fob.
 3. The method of claim 1 wherein thetransceiving device comprises the base station transceiving device. 4.The method of claim 1 wherein the transceiving device comprises theportable transceiving device.
 5. The method of claim 1 wherein thefrequency of the RF signal is varied over a plurality of discretefrequencies.
 6. The method of claim 1 wherein the other transceivingdevice determines the respective frequency having the maximum RSSIvalue.
 7. The method of claim 1 wherein the other transceiving devicemeasures the RSSI value of each varied frequency, determines therespective frequency having the maximum RSSI value, and transmits therespective frequency to the one transceiving device.
 8. The method ofclaim 1 wherein the one transceiving device transmits the RF signal tothe other transceiving device in response to an interrogation signal. 9.The method of claim 1 wherein the one transceiving device transmits theRF signal to the other transceiving device in response to an activeactivation signal.
 10. The method of claim 1 wherein the respectivefrequency is used to transmit subsequent RF messages by the one of theportable transceiving device or the base station transceiving deviceuntil a next respective frequency is determined.
 11. A self-aligningremote transmitter system for vehicle based RF applications, said systemcomprising: a base station receiving device for receiving a wirelessmessage for controlling an actuation of at least one accessory function;a portable receiving device for transmitting wireless message to saidvehicle based control module for activating said at least one vehicleaccessory function; wherein a RF signal is transmitted from one of saidportable or base station transceiving devices to the other of saidportable or base station transceiving devices, wherein the RF signal hasa frequency that varies during the transmission, wherein a RSSI value ismeasured at selected frequencies, wherein the other of said portable orbase station transceiving device transmits each RSSI value of eachvaried frequency to the one of said portable or base stationtransceiving device, wherein a respective frequency having a maximumRSSI value is determined by the one of said portable or base stationtransceiving devices, and wherein at least a portion of a subsequent RFmessage is transmitted from said one of said portable transceivingdevice or said base station transceiving device using a center frequencythat is tuned to the respective frequency having said maximum RSSIvalue.
 12. The system of claim 11 wherein said base station receivingdevice includes a vehicle-based keyless entry module for activatingvehicle entry functions.
 13. The system of claim 11 wherein said basestation receiving device includes a vehicle-based tire pressuremonitoring module for monitoring pressure of vehicle tires.
 14. Thesystem of claim 11 wherein said base station receiving device includes avehicle engine start/stop module for starting/stopping an engine of avehicle.
 15. The system of claim 11 wherein said portable receivingdevice includes a remote entry fob.
 16. The system of claim 11 whereinsaid portable receiving device includes a remote tire pressure sensordisposed is a vehicle tire.
 17. The system of claim 11 wherein saidportable receiving device includes a remote engine start/top device.